Helmets for protection against rifle bullets

ABSTRACT

A helmet shell is formed having an outer section of fibrous layers, a middle section of fibrous layers and an inner section of fibrous layers. The outer section layers contain high tenacity abrasive fibers in a resin matrix. The middle section layers contain high strength polyolefin fibers and are in the form of woven or knitted fabrics with a resin matrix. The inner section layers contain high strength polyolefin fibers and are in the form of non-woven fabrics with a resin matrix. The helmet is lightweight and resists penetration of rifle bullets.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.12/004,327, filed Dec. 20, 2007, now U.S. Pat. No. 8,853,105, the entiredisclosure of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to protective helmets which are useful formilitary, law enforcement and other applications. In particular, thisinvention relates to such helmets which provide protection against riflebullets.

Description of the Related Art

Protective helmets are well known. Such helmets have been used formilitary and non-military applications. Examples of the latter includelaw enforcement uses, sporting uses and other types of safety helmets.Protective helmets used for military and law enforcement uses, inparticular, need to be ballistic resistant.

Typical helmets are constructed to protect against bullet fragments.Protection against rifle bullets requires improvement over such helmetsin view of the significantly increased energy possessed by riflebullets. Helmets which protect against rifle bullets should berelatively lightweight and comfortable to wear. However, previouslysuggested helmets were relatively heavy.

Examples of rifle bullets against which protection is desired includethe NATO M80 ball, the AK 47, the AK 74, the Russian LPS and theEuropean SS 109, and the like.

The currently most popular military helmets are formed from aramidfibers, typically in the form of several layers of aramid fiberstogether with a resin material, such as a phenolic resin. Helmets formedof aramid fibers are disclosed, for example, in U.S. Pat. Nos.4,199,388, 4,778,638 and 4,908,877. Although such helmets in generalperform satisfactorily, they are fairly heavy. Also, such helmets do notprovide enhanced protection against rifle bullets. One problem withhelmets that are relatively heavy is that they are uncomfortable to thewearer. This may result in non-use or limited use of such helmets.

Examples of helmets which are designed to protect against projectilefragments (rather than rifle bullets) are set forth in copending U.S.patent application Ser. No. 11/706,719, filed Feb. 15, 2007, thedisclosure of which is incorporated herein by reference to the extentnot incompatible herewith.

It would be desirable to provide a helmet which has a reduced weight andalso is resistant to penetration by rifle bullets.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided a lightweightmolded helmet that is resistant to penetration by rifle bullets, thehelmet comprising a shell, the shell comprising from the outside to theinside:

a first plurality of fibrous layers, the fibrous layers comprising hightenacity abrasive fibers in a first resin matrix;

a second plurality of fibrous layers attached to the first plurality offibrous layers, the second plurality of fibrous layers comprising awoven or knitted network of high tenacity fibers in a second resinmatrix, the high tenacity fibers comprising polyolefin fibers; and

a third plurality of fibrous layers attached to the second plurality offibrous layers, the third plurality of fibrous layers comprising anon-woven network of high tenacity fibers in a third resin matrix, thehigh tenacity fibers comprising polyolefin fibers.

Also in accordance with this invention, there is provided a lightweightmolded helmet that is resistant to penetration by rifle bullets, thehelmet comprising a shell, the shell comprising from the outside to theinside:

a first plurality of fibrous layers, the first plurality of fibrouslayers comprising a woven network of glass fibers in a first resinmatrix, the first resin comprising a thermosetting resin;

a second plurality of fibrous layers attached to the first plurality offibrous layers, the second plurality of fibrous layers comprising awoven network of high tenacity fibers in a second resin matrix, the hightenacity fibers comprising polyethylene fibers, the second resincomprising a thermosetting resin or a thermoplastic resin; and

a third plurality of fibrous layers attached to the second plurality offibrous layers, the third plurality of fibrous layers comprising anon-woven network of high tenacity fibers in a third resin matrix, thehigh tenacity fibers comprising polyethylene fibers, the third resincomprising a thermoplastic resin,

the helmet having a total areal density of from about 3 to about 5pounds per square foot (14.6 to 24.4 kg/m²), and is resistant to riflebullets having energies of at least about 1600 joules.

Further in accordance with this invention, there is provided a methodfor forming a shell of a lightweight helmet that is resistant topenetration by rifle bullets, the method comprising the steps of:

supplying a first plurality of fibrous layers to a mold, the fibrouslayers comprising a network of high tenacity fibers in a first resinmatrix, the high tenacity fibers comprising abrasive fibers; the firstplurality of fibrous layers facing inwardly in the mold;

supplying a second plurality of fibrous layers to the mold, the secondplurality of fibrous layers comprising a woven network of high tenacityfibers in a second resin matrix, the high tenacity fibers comprisingpolyolefin fibers, the second plurality of fibrous layers overlying thefirst plurality of fibrous layers, the first and second resins beingcompatible such that the first and second plurality of fibrous layersare bondable to each other;

supplying a third plurality of fibrous layers to the mold, the thirdplurality of fibrous layers comprising a non-woven network of hightenacity fibers in a third resin matrix, the high tenacity fiberscomprising polyolefin fibers, the third plurality of fibrous layersoverlying the second plurality of fibrous layers; and

applying heat and pressure to the first plurality of fibrous layers, thesecond plurality of fibrous layers, and the third plurality of fibrouslayers to thereby form the helmet shell.

It has been discovered that lightweight molded helmets that areresistant to penetration by rifle bullets can be formed by employing anouter fiber layer section formed of high tenacity abrasive fibers in aresin matrix, a middle fiber layer section formed of woven or knittedhigh tenacity polyolefin fibers in a second resin matrix, and an innerfiber layer section formed of non-woven high tenacity polyolefin fibersin a third resin matrix. The resins in each of the first, second andthird fiber layer sections may be the same or different. Such helmetshave excellent ballistic resistance and are particularly useful toprevent penetration of high energy rifle bullets. At the same time, thehelmets are lightweight and are thus comfortable to wear.

DETAILED DESCRIPTION OF THE INVENTION

The protective helmets of this invention include a shell formed from afirst outer section comprising a plurality of layers of a network ofhigh tenacity abrasive fibers in a resin matrix, a second middle sectioncomprising a plurality of layers of a woven or knitted network of hightenacity polyolefin fibers in a resin matrix, and a third inner sectioncomprising a plurality of layers of a non-woven network of high tenacitypolyolefin fibers in a resin matrix.

For the purposes of the present invention, a fiber is an elongate bodythe length dimension of which is much greater that the transversedimensions of width and thickness. Accordingly, the term fiber includesmonofilament, multifilament, ribbon, strip, staple and other forms ofchopped, cut or discontinuous fiber and the like having regular orirregular cross-section. The term “fiber” includes a plurality of any ofthe foregoing or a combination thereof. A yarn is a continuous strandcomprised of many fibers or filaments.

As used herein, the term “high tenacity fibers” means fibers which havetenacities equal to or greater than about 7 g/d. Preferably, thesefibers have initial tensile moduli of at least about 150 g/d andenergies-to-break of at least about 8 J/g as measured by ASTM D2256. Asused herein, the terms “initial tensile modulus”, “tensile modulus” and“modulus” mean the modulus of elasticity as measured by ASTM 2256 for ayarn and by ASTM D638 for an elastomer or matrix material.

Preferably, the high tenacity fibers of the second and third sectionshave tenacities equal to or greater than about 10 g/d, more preferablyequal to or greater than about 15 g/d, even more preferably equal to orgreater than about 20 g/d, and most preferably equal to or greater thanabout 25 g/d. For high tenacity polyethylene fibers the preferredtenacities range from about 20 to about 55 g/d.

The cross-sections of fibers useful in this invention may vary widely.They may be circular, flat or oblong in cross-section. They also may beof irregular or regular multi-lobal cross-section having one or moreregular or irregular lobes projecting from the linear or longitudinalaxis of the filament. It is particularly preferred that the fibers be ofsubstantially circular, flat or oblong cross-section, most preferablythat the fibers be of substantially circular cross-section.

The yarns of the high tenacity fibers used herein may be of any suitabledenier, such as, for example, about 50 to about 5000 denier, morepreferably from about 200 to about 5000 denier, still more preferablyfrom about 650 to about 3000 denier, and most preferably from about 800to about 1500 denier.

Preferably, at least about 50% by weight, more preferably at least about75% by weight, and most preferably all or substantially all of thefibers in the first plurality of fibrous layers are the high tenacityabrasive fibers. Similarly, preferably, at least about 50% by weight,more preferably at least about 75% by weight, and most preferably all orsubstantially all of the fibers in the second plurality of fibrouslayers are the high tenacity polyolefin fibers. Also, preferably, atleast about 50% by weight, more preferably at least about 75% by weight,and most preferably all or substantially all of the fibers in the thirdplurality of fibrous layers are the high tenacity polyolefin fibers.

In accordance with the invention, the helmet shell is formed from layersof different ballistic resistant materials. The helmet comprises atleast three sections or groups of fibrous layers. These are an outerfacing group of layers, a middle group of layers, and an inner facinggroup of layers.

The outer group of fibrous layers is selected such that it has abrasivecharacteristics such that it deforms the bullet, or strips the bulletjacket and/or otherwise destabilizes the bullet. The outer group offibrous layers are formed from abrasive fibers. These fibers arepreferably inorganic fibers that have a tensile strength of at leastabout 2.0 GPa, preferably at least about 2.4 GPa, more preferably atleast about 3.4 GPa, and most preferably at least about 4.0 GPa.Examples of abrasive fibers useful herein include glass fibers, graphitefibers, silicon carbide fibers, boron carbide fibers, and the like, andmixtures thereof. Examples of such fibers are described, for example, incommonly assigned copending U.S. patent application Ser. No. 10/957,773,filed Oct. 4, 2004 (which corresponds to published PCT applicationWO2007/005043), the disclosure of which application is expresslyincorporated herein by reference to the extent not inconsistentherewith. Preferably, the abrasive fibers are glass fibers.

Various types of glass fibers may be used herein, including Types E andS fibers. Examples of woven fiberglass fabrics are those designated asstyles 1528, 3731, 3733, 7500, 7532, 7533, 7580, 7624, 7628 and 7645,which are available from Hexcel of Anderson, S.C., USA.

A benefit of using fiber glass as the abrasive fibers is that the costof the helmet can be significantly decreased since the fiber glass costsonly a fraction compared to the cost of the polyolefin fabrics.

The outer group of fibrous layers is preferably in the form of aplurality of woven fabric layers. However, the outer group of fibrouslayers may alternatively be in the form of knitted or non-woven fabriclayers. Examples of the latter are unidirectionally oriented fiberlayers and random or felted fiber layers. The fiber network layers ofthe outer group are preferably in the same fabric format (e.g., woven,knitted or non-woven). Alternatively, there may be a mixture of the typeof fabrics in the outer group of layers (woven, knitted, and/ornon-woven fabrics. Woven fabrics are preferred and fabrics of any weavepattern may be employed, such as plain weave, basket weave, twill,satin, three dimensional woven fabrics, and any of their severalvariations.

The layers of the outer group of fibrous layers also comprise a resinmatrix. Examples of the resin materials are discussed below.

As mentioned above, the fibers in the middle and inner groups of fiberscomprise polyolefin fibers, preferably high tenacity polyethylene fibersand/or high tenacity polypropylene fibers. Most preferably, thepolyolefin fibers are high tenacity polyethylene fibers, also known asextended chain polyethylene fibers or highly oriented high molecularweight polyethylene fibers.

U.S. Pat. No. 4,457,985 generally discusses high molecular weightpolyethylene fibers and polypropylene fibers, and the disclosure of thispatent is hereby incorporated by reference to the extent that it is notinconsistent herewith. In the case of polyethylene fibers, suitablefibers are those of weight average molecular weight of at least about150,000, preferably at least about one million and more preferablybetween about two million and about five million. Such high molecularweight polyethylene fibers may be spun in solution (see U.S. Pat. Nos.4,137,394 and 4,356,138), or a filament spun from a solution to form agel structure (see U.S. Pat. No. 4,413,110, German Off. No. 3,004, 699and GB Patent No. 2051667), or the polyethylene fibers may be producedby a rolling and drawing process (see U.S. Pat. No. 5,702,657). As usedherein, the term polyethylene means a predominantly linear polyethylenematerial that may contain minor amounts of chain branching or comonomersnot exceeding about 5 modifying units per 100 main chain carbon atoms,and that may also contain admixed therewith not more than about 50weight percent of one or more polymeric additives such asalkene-1-polymers, in particular low density polyethylene, polypropyleneor polybutylene, copolymers containing mono-olefins as primary monomers,oxidized polyolefins, graft polyolefin copolymers and polyoxymethylenes,or low molecular weight additives such as antioxidants, lubricants,ultraviolet screening agents, colorants and the like which are commonlyincorporated.

High tenacity polyethylene fibers are commercially available and aresold under the trademark SPECTRA® by Honeywell International Inc. ofMorristown, N.J., U.S.A. Polyethylene fibers from other sources may alsobe used.

Depending upon the formation technique, the draw ratio and temperatures,and other conditions, a variety of properties can be imparted to thesefibers. The tenacity of the polyethylene fibers is at least about 7 g/d,preferably at least about 15 g/d, more preferably at least about 20 g/d,still more preferably at least about 25 g/d and most preferably at leastabout 30 g/d. Similarly, the initial tensile modulus of the fibers, asmeasured by an Instron tensile testing machine, is preferably at leastabout 300 g/d, more preferably at least about 500 g/d, still morepreferably at least about 1,000 g/d and most preferably at least about1,200 g/d. These highest values for initial tensile modulus and tenacityare generally obtainable only by employing solution grown or gelspinning processes. Many of the filaments have melting points higherthan the melting point of the polymer from which they were formed. Thus,for example, high molecular weight polyethylene of about 150,000, aboutone million and about two million molecular weight generally havemelting points in the bulk of 138° C. The highly oriented polyethylenefilaments made of these materials have melting points of from about 7°C. to about 13° C. higher. Thus, a slight increase in melting pointreflects the crystalline perfection and higher crystalline orientationof the filaments as compared to the bulk polymer.

Similarly, highly oriented high molecular weight polypropylene fibers ofweight average molecular weight at least about 200,000, preferably atleast about one million and more preferably at least about two millionmay be used. Such extended chain polypropylene may be formed intoreasonably well oriented filaments by the techniques prescribed in thevarious references referred to above, and especially by the technique ofU.S. Pat. No. 4,413,110. Since polypropylene is a much less crystallinematerial than polyethylene and contains pendant methyl groups, tenacityvalues achievable with polypropylene are generally substantially lowerthan the corresponding values for polyethylene. Accordingly, a suitabletenacity is preferably at least about 8 g/d, more preferably at leastabout 11 g/d. The initial tensile modulus for polypropylene ispreferably at least about 160 g/d, more preferably at least about 200g/d. The melting point of the polypropylene is generally raised severaldegrees by the orientation process, such that the polypropylene filamentpreferably has a main melting point of at least 168° C., more preferablyat least 170° C. The particularly preferred ranges for the abovedescribed parameters can advantageously provide improved performance inthe final article. Employing fibers having a weight average molecularweight of at least about 200,000 coupled with the preferred ranges forthe above-described parameters (modulus and tenacity) can provideadvantageously improved performance in the final article.

The network of high strength fibers polyolefin fibers of the middlesection of fibrous layers are in the form of a woven or knitted fabric.Woven fabrics are preferred and fabrics of any weave pattern may beemployed, such as plain weave, basket weave, twill, satin, threedimensional woven fabrics, and any of their several variations. Plainweave fabrics are preferred and more preferred are plain weave fabricshaving an equal warp and weft count.

In one embodiment, the woven fabric preferably has between about 15 andabout 55 ends per inch (about 5.9 to about 21.6 ends per cm) in both thewarp and fill directions, and more preferably between about 17 and about45 ends per inch (about 6.7 to about 17.7 ends per cm). The yarnspreferably have a denier of from about 375 to about 1300. The result isa woven fabric weighing preferably between about 5 and about 19 ouncesper square yard (about 169.5 to about 644.1 g/m²), and more preferablybetween about 5 and about 11 ounces per square yard (about 169.5 toabout 373.0 g/m²). Examples of such fabrics are those designated asSPECTRA® fabric styles 902, 903, 904, 952, 955 and 960. Other examplesincluded fabrics formed from basket weaves, such as SPECTRA® fabricstyle 912. The foregoing fabrics are available, for example, fromHexcel. As those skilled in the art will appreciate, the fabricconstructions described here are exemplary only and not intended tolimit the invention thereto.

Where knitted fabrics are used in the middle section of fibrous layers(or in the outer section of fibrous layers), different knit structuresmay be employed. Knit structures are constructions composed ofintermeshing loops. Oriented knitted structures are preferred as theyuse straight inlaid yarns held in place by fine denier knitted stitches.The yarns are absolutely straight without the crimp effect found inwoven fabrics due to the interlacing effect on the yarns. These laid inyarns can be oriented in a monoaxial, biaxial or multiaxial directiondepending on the engineered requirements. It is preferred that thespecific knit equipment used in laying in the load bearing yarns is suchthat the yarns are not pierced through.

The layers of the middle group of fibrous layers likewise also comprisea resin matrix. Examples of the resin materials are discussed below.

As mentioned above, the inner group of fibrous layers also comprise hightenacity polyolefin fibers, most preferably high tenacity polyethylenefibers. These fibrous layers are in the form of non-woven networks offibers, such as such as plies of unidirectionally oriented fibers, orfibers which are felted in a random orientation. Where unidirectionallyoriented fibers are employed, preferably they are used in a cross-plyarrangement in which one layer of fibers extend in one direction and asecond layer of fibers which extend in a direction 90° from the firstfibers. Where the individual plies are unidirectionally oriented fibers,the successive plies are preferably rotated relative to one another, forexample at angles of 0°/90°, 0°/90/0°/90 or 0°/45°/90°/45°/0° or atother angles. Where the networks of fibers are in the form of a felt,they may be needle punched felts. A felt is a non-woven network ofrandomly oriented fibers, preferably at least one of which is adiscontinuous fiber, preferably a staple fiber having a length rangingfrom about 0.25 inch (0.64 cm) to about 10 inches (25.4 cm). These feltsmay be formed by several techniques known in the art, such as by cardingor fluid laying, melt blowing and spin laying. The network of fibers isconsolidated mechanically such as by needle punching, stitch-bonding,hydro-entanglement, air entanglement, spun bond, spun lace or the like,chemically such as with an adhesive, or thermally with a fiber to pointbond or a blended fiber with a lower melting point. The preferredconsolidation method is needle punching alone or followed by one of theother methods. The preferred felt is a needle punched felt. Wherenon-woven structures are employed in the first group of abrasive fibers,they may have similar constructions to those mentioned herein.

The layers of the inner group of fibrous layers likewise also comprise aresin matrix. Examples of the resin materials are discussed below.

The fibrous layers of each of the outer, middle and inner sections ofthe helmet shell also include a resin matrix. The resin matrix for thefiber plies may be formed from a wide variety of elastomeric and othermaterials having desired characteristics. In one embodiment, elastomericmaterials used in such matrix possess initial tensile modulus (modulusof elasticity) equal to or less than about 6,000 psi (41.4 MPa) asmeasured by ASTM D638. More preferably, the elastomer has initialtensile modulus equal to or less than about 2,400 psi (16.5 MPa). Mostpreferably, the elastomeric material has initial tensile modulus equalto or less than about 1,200 psi (8.23 MPa). These resinous materials aretypically thermoplastic in nature but thermosetting materials are alsouseful.

The resin matrix may alternatively be selected to have a high tensilemodulus when cured, such as at least about 1×10⁶ psi (6895 MPa) asmeasured by ASTM D638. Examples of such materials are disclosed, forexample, in U.S. Pat. No. 6,642,159, the disclosure of which isexpressly incorporated herein by reference to the extent notinconsistent herewith.

A wide variety of materials may be utilized as the resin matrix for eachof the outer, middle and inner section of fibrous layers, includingthermoplastic and thermosetting resins. For example, any of thefollowing materials may be employed: polybutadiene, polyisoprene,natural rubber, ethylene-propylene copolymers, ethylene-propylene-dieneterpolymers, polysulfide polymers, thermoplastic polyurethanes,polyurethane elastomers, chlorosulfonated polyethylene, polychloroprene,plasticized polyvinylchloride using dioctyl phthalate or otherplasticizers well known in the art, butadiene acrylonitrile elastomers,poly(isobutylene-co-isoprene), polyacrylates, polyesters, polyethers,fluoroelastomers, silicone elastomers, thermoplastic elastomers, andcopolymers of ethylene. Examples of thermosetting resins include thosewhich are soluble in carbon-carbon saturated solvents such as methylethyl ketone, acetone, ethanol, methanol, isopropyl alcohol,cyclohexane, ethyl acetone, and combinations thereof. Among thethermosetting resins are vinyl esters, styrene-butadiene blockcopolymers, diallyl phthalate, phenolic resins such as phenolformaldehyde, polyvinyl butyral, epoxy resins, polyester resins,thermosetting polyurethane resins, and mixtures thereof, and the like.Included are those resins that are disclosed in the aforementioned U.S.Pat. No. 6,642,159. Preferred thermosetting resins include epoxy resins,urethane resins, polyester resins, vinyl ester resins, phenolic resins,and mixtures thereof. Preferred thermosetting resins for polyethylenefiber fabrics include at least one vinyl ester, diallyl phthalate, andoptionally a catalyst for curing the vinyl ester resin. Otherthermosetting resins include melamine resins, acrylate resins, siliconeresins, polyurea resins, and the like.

One preferred group of resins are thermoplastic polyurethane resins.Another preferred group are elastomeric materials that are blockcopolymers of conjugated dienes and vinyl aromatic copolymers. Butadieneand isoprene are preferred conjugated diene elastomers. Styrene, vinyltoluene and t-butyl styrene are preferred conjugated aromatic monomers.Block copolymers incorporating polyisoprene may be hydrogenated toproduce thermoplastic elastomers having saturated hydrocarbon elastomersegments. The polymers may be simple tri-block copolymers of the typeR−(BA)_(x)(x=3-150); wherein A is a block from a polyvinyl aromaticmonomer and B is a block from a conjugated diene elastomer. A preferredresin matrix is an isoprene-styrene-isoprene block copolymer, such asKraton® D1107 isoprene-styrene-isoprene block copolymer available fromKraton Polymer LLC. These resins may be dispersed in water or in anorganic solvent. One type of thermoplastic polyurethane resin is acopolymer mix of polyurethane resins dispersed in water.

The resin material may be compounded with fillers such as carbon black,silica, etc and may be extended with oils and vulcanized by sulfur,peroxide, metal oxide or radiation cure systems using methods well knownto rubber technologists. Blends of different resins may also be used.

Preferably, the resin matrix in each of the plurality of fibrous layersare either the same as or are compatible with the resin matrix in theother plurality or pluralities of fibrous layers. By “compatible” ismeant that the various layers may be bonded together by chemical meansor mechanical means. For example, the chemistry of the resins of variousgroups of layers is preferably compatible such that various layers canbe processed under the same molding pressure, temperature and moldingduration conditions. This ensures that the helmet shell can be molded inone efficient cycle. In one embodiment, the resin of the outer group offibrous layers is compatible with the resin of the middle group offibrous layers such that those layers bond together. Preferably, theresin in the outer group of fibrous layers and the resin in the middlegroup of fibrous layers are chemically the same, and the resin in theinner group of fibrous layers is chemically different from the otherresins.

Preferred resins for the outer group of fibrous layers are thermosettingresins, more preferably vinyl ester resins. Preferred resins for themiddle group of fibrous layers are thermosetting or thermoplasticresins, more preferably vinyl ester resins when a thermosetting resin isemployed. Also preferred for the middle group of fibrous layers arethermoplastic polyurethane resins and/or styrene-isoprene-styrene blockcopolymers. Preferred resins for the inner group of fibrous layers arethermoplastic resins, more preferably thermoplastic polyurethane resinsand/or styrene-isoprene-styrene block copolymers.

The proportion of the resin matrix material to fiber in each of thethree sections of the helmet shell may vary widely depending. Ingeneral, the resin matrix material preferably forms about 1 to about 98percent by weight, more preferably from about 5 to about 95 percent byweight, and still more preferably from about 5 to about 40 percent byweight, of the total weight of the fibers and resin matrix in thelayers. The above percentages are based on the consolidated fabrics.Most preferably, the resin in the outer group of fibrous layerscomprises from about 5 to about 25 weight percent of the total weight ofthe outer fibrous layers; the resin in the middle group of fibrouslayers comprises from about 10 to about 25 weight percent of the totalweight of the middle fibrous layers; and the resin in the inner group offibrous layers comprises from about 10 to about 40 weight percent of thetotal weight of the inner fibrous layers.

Preferably, each of the plurality of fibrous layers is coated orimpregnated with the resin matrix prior to molding, so as to formprepreg fabrics. In general, the fibrous layers of the invention arepreferably formed by constructing a fiber network initially (e.g.,starting with a woven, knitted or non-woven fabric layer) and thencoating the network with the matrix composition. As used herein, theterm “coating” is used in a broad sense to describe a fiber networkwherein the individual fibers either have a continuous layer of thematrix composition surrounding the fibers or a discontinuous layer ofthe matrix composition on the surfaced of the fibers. In the formercase, it can be said that the fibers are fully embedded in the matrixcomposition. The terms coating and impregnating are interchangeably usedherein. Although it is possible to apply the resin matrix to resin-freefibrous layers while in the mold, this is less desirable since theuniformity of the resin coating may be difficult to control.

The matrix resin composition may be applied in any suitable manner, suchas a solution, dispersion or emulsion, onto the fibrous layers. Thematrix-coated fiber network is then dried. The solution, dispersion oremulsion of the matrix resin may be sprayed onto the filaments.Alternatively, the fibrous layer structure may be coated with theaqueous solution, dispersion or emulsion by dipping or by means of aroll coater or the like. After coating, the coated fibrous layer maythen be passed through an oven for drying in which the coated fibernetwork layer or layers are subjected to sufficient heat to evaporatethe water or other liquid in the matrix composition. The coated fibrousnetwork may then be placed on a carrier web, which can be a paper or afilm substrate, or the fabrics may initially be placed on a carrier webbefore coating with the matrix resin. The substrate and the resin matrixcontaining fabric layer or layers can then be wound up into a continuousroll in a known manner.

The fiber networks can be constructed via a variety of methods. In thecase of unidirectionally aligned fiber networks, yarn bundles of thehigh tenacity filaments may be supplied from a creel and led throughguides and one or more spreader bars into a collimating comb prior tocoating with the matrix material. The collimating comb aligns thefilaments coplanarly and in a substantially unidirectional fashion.

Following coating of the fabric layers with the resin matrix, the layersmay be pre-formed in a helmet shape, with the fibrous layers either notbonded to each other or only slightly attached to each other for ease ofhandling. Such pre-forming aids in the final molding process.

The number of layers in each section of the plurality of fibrous layersmay vary widely, depending on the type of helmet desired, the desiredperformance and the desired weight. For example, the number of layers ineach section of the plurality of fibrous layers may range from about 2to about 100 layers, more preferably from about 2 to about 85 layers,and most preferably from about 2 to about 65 layers. The number oflayers in each section of the plurality of fibrous layers may bedifferent or may be the same. The layers may be of any suitablethickness. For example, each layer of a section of the plurality offibrous layers may have a thickness of from about 1 mil to about 40 mils(25 to 1016 μm), more preferably from about 3 to about 30 mils (76 to762 μm), and most preferably from about 5 to about 20 mils (127 to 508μm). The thickness of each layer of each plurality of fibrous networksmay be the same or different.

The areal density of each layer in each section of the plurality offibrous layers may vary widely but is usually chosen so that the overallweight of the helmet is within an acceptable range for the comfort andprotection of the wearer. For example, the areal density of each layerin the outer section of the plurality of fibrous layers preferably mayrange from about 5 to about 35 oz/yd² (about 169.5 to about 1186.5g/m²), more preferably from about 5 to about 25 oz/yd² (about 169.5 toabout 847.5 g/m²). The areal density of each layer in the middle sectionof the plurality of fibrous layers preferably may range from about 5 toabout 65 oz/yd² (about 169.5 to about 2203.5 g/m²), more preferably fromabout 5 to about 14 oz/yd² (about 169.5 to about 474.7 g/m²). The arealdensity of each layer in the inner section of the plurality of fibrouslayers preferably may range from about 1 to about 90 oz/yd² (about 33.9to about 3051 g/m²), more preferably from about 1 to about 7 oz/yd²(about 33.9 to about 237.3 g/m²). The areal densities of the fibrouslayers in each of the outer, middle and inner sections may be the sameor different.

The weight ratio of the layers may vary as desired. The outer group offibrous layers may be present in an amount, based on the total weight ofthe helmet shell, of from about 2 to about 35 weight percent, morepreferably from about 5 to about 15 weight percent, and most preferablynot more than about 10 weight percent. The middle group of fibrouslayers may be present in an amount, based on the total weight of thehelmet shell, of from about 2 to about 65 weight percent, morepreferably from about 10 to about 50 weight percent, and most preferablynot more than about 40 weight percent. The inner group of fibrous layersmay be present in an amount, based on the total weight of the helmetshell, of from about 5 to about 96 weight percent, more preferably fromabout 20 to about 90 weight percent, and most preferably at least about60 weight percent.

As mentioned above, the helmet shells of this invention are“lightweight”. By lightweight is meant that the total areal density isless than about 5 pounds per square foot (24.4 kg/m²). Preferably, thetotal areal density of the helmet shells range from about 3 to about 5pounds per square (about 14.6 to about 24.4 kg/m²).

One type of helmet shape that has been employed in military applicationsis known by the acronym ACH (Advanced Combat Helmet). Desirably, suchhelmets (although not rifle bullet resistant) have a weight in the rangeof from about 900 to about 1500 grams, and more preferably from about1000 to about 1300 grams.

To form the helmet shells of this invention, stacks of each section ofthe fibrous layers are placed in a suitable mold of any desired shape.It is desirable to form the shell from the three sections in a singlemolding step for efficiency. However, if desired one or two of thesections may be first molded before the other sections are introducedinto the mold. The mold may be of any desired shape, such as a bowlshape, an oval shape, etc.

Preferably, first a stack of loosely bonded or unbonded layers formingthe outer section of the shell is placed into the mold. Such stack maybe pre-formed to approximately the desired shape. Next, a stack ofloosely bonded or unbonded layers forming the middle section of theshell is placed on top of the outer section layers. Following this, astack of loosely bonded or unbonded layers forming the inner section ofthe shell is placed on top of the middle section layers. Whereunidirectionally oriented fabrics are employed as the non-woven fabriclayers of the inner section of the shell, two or more layers arepreferably first cross-plied with each other, such as at angles of0°/90°, 0°/90°/0°/90°, etc. These cross-plied structures (commonlyreferred to as shield products) are then introduced into the mold. Thestack of the middle and inner sections of the helmet may also bepre-formed to approximately the desired shape.

No adhesive is required to be used between the individual layers orsections of layers of the high tenacity fibers, since the resin orresins of the individual layers provide the requisite bonding betweenthe layers. However, a separate adhesive layer or layers may be used ifdesired.

Care should be taken to completely and uniformly fill the mold and placeall of the layers in the proper orientation. This ensures uniformperformance throughout the helmet shell. If the combined volume of thefibrous sections is more than the helmet mold can handle, the mold willnot close and hence the helmet will not be molded. If the combinedvolume of the materials is less than the volume of the mold, althoughthe mold will close the material may not be molded due to lack ofmolding pressure.

Once the mold is properly loaded with the requisite number and type offibrous layers, the helmet shell can be molded under the desired moldingconditions. These conditions can be similar to those employed in moldingseparate layers of aramid fabrics and separate layers of polyethylenefabrics. For example, the molding temperature may range from about 65 toabout 250° F., more preferably from about 90 to about 330°F., and mostpreferably from about 120 to about 320°F. The clamp molding pressure mayrange, for example, from about 10 to about 500 tons (10.2 to 508 metrictons), more preferably from about 50 to about 350 tons (50.8 to 356metric tons), and most preferably from about 100 to about 200 tons (102to 203 metric tons). The molding times may range from about 5 to about60 minutes, more preferably from about 10 to about 35 minutes, and mostpreferably from about 15 to about 25 minutes.

Under the desired conditions of molding, the resin or resins present inthe fibrous networks is cured in the case of thermosetting resins. Thisresults in strong bonding of the individual layers and groups of layersinto the desired helmet shape as an integral, monolithic molding. It isbelieved that the thermosetting resins of each set of fabrics are bondedat their interfaces by cross-linking of the resins. For thermoplasticresins the helmet is cooled down below the softening temperature of theresin and then pull out from the mold. Under heat and pressure, thethermoplastic resins flow between the fabric layers, also resulting inan integral, monolithic molding. During cooling the molding pressure ismaintained. The molded product is thereafter taken from the mold and thepart is trimmed, if necessary.

The fabrics used in the composite structure are relatively thin yet verystrong. The preferred thickness of the individual fabric layers are fromabout 1 to about 36 mils (25 to 911 μm), more preferably from about 3 toabout 28 mils (76.2 to 711 μm), and most preferably from about 5 toabout 23 mils (127 to 584 μm).

As mentioned earlier, the helmets of this invention are capable ofpreventing penetration of rifle bullets. Such bullets have very highenergy levels. The helmets of this invention are capable of preventingpenetration by bullets that have energy levels of at least about 1600joules, more preferably bullets that have energy levels of from about1600 to about 4000 joules, and most preferably bullets that have energylevels of from about 1700 to about 3000 joules.

The following is a list of various bullets and their energy levels, withthe velocities and energy measured at the muzzle. It can be seen thatthe rifle bullets have much higher energy levels than handgun bullets,and are thus more difficult to stop from penetrating helmets.

TABLE 1 Kinetic Energy of Bullets Energy, Bullet Mass, grain (g)Velocity, mps Joules 9 MM FMJ 124 (g) 373 ± 10  537 357 158 (9.5 g) 440± 10  958 44 Mag 240 (15 g) 441 ± 10 1510 AK 47 128 (8 g) 900 ± 10 1960NATO (M80) (9.5 g) 810 ± 10 3000 AK74 (3.4 g) 750 ± 10 1700 LPS 179(11.6 g) 804 ± 10 3814

Even though the helmets of this invention are lightweight, due to theirunique construction they are capable of preventing penetration of highenergy rifle bullets. This combination of desirable weight and ballisticresistance means that the helmets would be more readily used bypersonnel who need to be protected from high energy level threats.

The helmet structure can be adapted to receive a variety of attachmentsas desired. For example, the helmet may be formed with grooves or builtin channels to facilitate attachment of desired gear.

While not being bound to any particular theory, it is believed that theouter section containing fibrous layers of abrasive fibers acts todeform the rifle bullet and its jacket. The middle section containinglayers of woven or knitted high tenacity polyolefin fibers peels awaythe bullet jacket or outer casing. The inner section containing layersof non-woven high tenacity polyolefin fibers deforms the rest of thebullet and captures it, thereby preventing penetration through thehelmet.

The following non-limiting examples are presented to provide a morecomplete understanding of the invention. The specific techniques,conditions, materials, proportions and reported data set forth toillustrate the principles of the invention are exemplary and should notbe construed as limiting the scope of the invention. All percents are byweight, unless otherwise stated.

EXAMPLES Example 1

A helmet shell is formed from three different sections of high tenacityfibers. The outer layers are formed of fiber glass in a wovenconstruction (Style 7628 from Hexcel, which is a plain weave 17×12 endsper inch (6.7×4.7 ends per cm). The individual woven fiber glass layersare coated with a vinyl ester resin (Derakane 411-25 resin from AshlandChemical) by dipping the woven fabric into a container of the resin inacetone solvent and a curing agent. After drying, the woven fiber glasslayers are found to have 10 percent by weight of the vinyl ester resin.The areal density of each layer is 200 g/m². A total of 2 layers of thewoven fiber glass composite are loosely stacked and pre-formed into theapproximate shape of a helmet.

The middle layers of the helmet shell are formed from a woven hightenacity polyethylene fiber (Spectra® 900 from Honeywell InternationalInc.). These fibers have a tenacity of 30 g/d. The woven fabric is style903 from Hexcel which is a plain weave 21×21 ends per inch (8.3×8.3 endsper cm) fabric. Individual woven polyethylene fiber layers are coatedwith the same vinyl ester resin as used with the fiber glass layers bydipping the fabric into a container of the resin solution. After drying,the woven polyethylene fiber layers are found to have 20 percent byweight of the vinyl ester resin. The areal density of each layer is 296g/m². A total of 2 layers of the woven high tenacity polyethylene fibercomposites are loosely stacked and pre-formed into the approximate shapeof a helmet.

The inner layers of the helmet shell are formed from unidirectionallyoriented high tenacity polyethylene fibers (Spectra® 3000 from HoneywellInternational Inc.) having a denier of 1300. A web of theunidirectionally oriented fibers are passed through a coating bathcontaining a thermoplastic polyurethane resin in water, and after dryingthe resin is found to comprise 16 percent by weight of the non-wovenfabric layer. Four layers of these layers are cross-plied at0°/90°/0°/90° and laminated together to form a four-ply shield product.The areal density of the four-ply composite is 257 g/m². A total of 67layers of the four-ply layers are loosely stacked together, with thefiber orientation of adjacent fiber layers being offset 90° from eachother. The fiber layers are pre-formed into the approximate shape of ahelmet.

The three sections of the helmet shell are introduced into a mold havingthe desired helmet shape (ACH mold), with the outer layers being firstplaced into the mold, followed by the middle layers and then followed bythe inner layers. The stack of layers is molded under 190 ton (193metric ton) clamp pressure at 90° F. (32° C.) for 15 minutes of heating,followed by a cool down to 220° F. (104° C.) for 15 minutes. Afterreleasing from the mold, the edges of the helmet shell are trimmed. Thetotal areal density of the helmet shell is 3.75 pounds per square foot(18.31 kg/m²).

The helmet shell is tested against rifle bullets (AK47, AK74 and NATOBall) under MIL-STD-662F standard and are found to resist penetration ofsuch bullets.

Example 2

A helmet was prepared as in Example 1, except that the resin used in themiddle layers is the same type of thermoplastic polyurethane resin usedin the layers of the inner section. The resin content of the middlefibrous layers is 20 weight percent.

The helmet shell is tested as in Example 1, and similar results arenoted.

Example 3

A helmet is prepared as in Example 1, except that the resin in the innerlayers is a styrene-isoprene-styrene block copolymer (Kraton D-1107).The resin content of the inner fibrous layers was 17 weight percent. Thehelmet shell is tested as in Example 1, and similar results are noted.

The helmets of this invention are lightweight and yet have excellentresistance to rifle bullets. The helmets also have excellent impactresistance and structural rigidity. The helmets are useful in militaryand non-military applications, such as law enforcement helmets, sportinghelmets and other types of safety helmets.

Having thus described the invention in rather full detail, it will beunderstood that such detail need not be strictly adhered to but thatfurther changes and modifications may suggest themselves to one skilledin the art, all falling within the scope of the invention as defined bythe subjoined claims.

What is claimed:
 1. A lightweight molded helmet that is resistant to penetration by rifle bullets, said helmet comprising a shell, said shell comprising from the outside to the inside: a first plurality of fibrous layers, said fibrous layers comprising high tenacity abrasive fibers impregnated with a first resin matrix; a second plurality of fibrous layers attached to said first plurality of fibrous layers, said second plurality of fibrous layers comprising a woven or knitted network of high tenacity fibers impregnated with a second resin matrix, said high tenacity fibers comprising polyolefin fibers; and a third plurality of fibrous layers attached to said second plurality of fibrous layers, said third plurality of fibrous layers comprising a non-woven network of high tenacity fibers impregnated with a third resin matrix, said high tenacity fibers comprising polyolefin fibers.
 2. The helmet of claim 1 wherein said second and third plurality of fibrous layers comprise polyethylene fibers.
 3. The helmet of claim 2 wherein said third plurality of fibrous layers comprises unidirectionally oriented fiber layers that are oriented with respect to one another.
 4. The helmet of claim 1 wherein the fibers of the first plurality of fibrous layers are fully embedded in the first resin matrix; the fibers of the second plurality of fibrous layers are fully embedded in the second resin matrix; and the fibers of the third plurality of fibrous layers are fully embedded in the third resin matrix.
 5. The helmet of claim 4 wherein said first resin comprises a thermosetting resin, said second resin comprises a thermosetting or thermoplastic resin, and said third resin comprises a thermoplastic resin.
 6. The helmet of claim 5 wherein said thermosetting resins are selected from the group consisting of epoxy resins, urethane resins, polyester resins, vinyl ester resins, phenolic resins, and mixtures thereof.
 7. The helmet of claim 5 wherein said thermoplastic resins are selected from the group consisting of polyurethane resins, block copolymers of a conjugated diene and a vinyl aromatic monomer, and mixtures thereof.
 8. The helmet of claim 1 wherein said first resin and said second resin are compatible such that said first and second plurality of fibrous layers are bonded together.
 9. The helmet of claim 1 wherein said first resin and said second resin are chemically the same and said third resin is chemically different from said first and second resins.
 10. The helmet of claim 1 wherein said first and second resins each comprise a vinyl ester resin.
 11. The helmet of claim 10 wherein said third resin comprises a thermoplastic polyurethane resin.
 12. The helmet of claim 10 wherein said third resin comprises a styrene-isoprene-styrene lock copolymer.
 13. The helmet of claim 1 wherein said abrasive fibers comprise glass fibers.
 14. The helmet of claim 1 wherein said first plurality of fibrous layers comprises from about 2 to about 35 weight percent of said shell, said second plurality of fibrous layers comprises from about 2 to about 65 weight percent of said shell, and said third plurality of fibrous layers comprises from about 5 to about 96 weight percent of said shell.
 15. The helmet of claim 1 wherein said first plurality of fibrous layers comprises woven fabrics.
 16. The helmet of claim 1 wherein the areal density of said fibrous layers of said first plurality of fibrous layers is from about 5 to about 35 oz./yd² (169.5 to 1186.5 g/m²), the areal density of said fibrous layers of said second plurality of fibrous layers is from about 5 to about 65 oz./yd² (169.5 to 2203 g/m²), and the areal density of said fibrous layers of said third plurality of fibrous layers is from about 1 to about 90 oz./yd² (33.9 to 3051 g/m²).
 17. The helmet of claim 1 wherein the areal density of said fibrous layers of said first plurality of fibrous layers is from about 5 to about 25 oz./yd² (169.5 to 847.5 g/m²), the areal density of said fibrous layers of said second plurality of fibrous layers is from about 5 to about 14 oz./yd² (169.5 to 474.7 g/m²), and the areal density of said fibrous layers of said third plurality of fibrous layers is from about 1 to about 7 oz./yd² (33.9 to 237.3 g/m²).
 18. The helmet of claim 1 wherein said first resin comprises from about 5 about 25 weight percent of the total weight of said first plurality of fibrous layers, said second resin comprises from about 10 to about 25 weight percent of the total weight of said second plurality of fibrous layers, and said third resin comprises from about 10 to about 40 weight percent of the total weight of said third plurality of fibrous layers.
 19. A lightweight molded helmet that is resistant to penetration by rifle bullets, said helmet comprising a shell, said shell comprising from the outside to the inside: a first plurality of fibrous layers, said first plurality of fibrous layers comprising a woven network of high tenacity glass fibers impregnated with and fully embedded in a first resin matrix, said first resin comprising a thermosetting resin; a second plurality of fibrous layers attached to said first plurality of fibrous layers, said second plurality of fibrous layers comprising a woven network of high tenacity fibers impregnated with and fully embedded in a second resin matrix, said high tenacity fibers comprising polyethylene fibers, said second resin comprising a thermosetting resin or thermoplastic resin; and a third plurality of fibrous layers attached to said second plurality of fibrous layers, said third plurality of fibrous layers comprising a non-woven network of high tenacity fibers impregnated with and fully embedded in a third resin matrix, said high tenacity fibers comprising polyethylene fibers, said third resin comprising a thermoplastic resin, said helmet having a total areal density of from about 3 to about 5 pounds per square foot (14.6 to 24.4 kg/m²), and is resistant to rifle bullets having energies of at least about 1600 joules.
 20. A method for forming a shell of a lightweight helmet that is resistant to penetration by rifle bullets, said method comprising the steps of: supplying a first plurality of fibrous layers to a mold, said fibrous layers comprising a network of high tenacity fibers impregnated with a first resin matrix, said high tenacity fibers comprising abrasive fibers; said first plurality of fibrous layers facing inwardly in said mold; supplying a second plurality of fibrous layers to said mold, said second plurality of fibrous layers comprising a woven network of high tenacity fibers impregnated with a second resin matrix, said high tenacity fibers comprising polyolefin fibers, said second plurality of fibrous layers overlying said first plurality of fibrous layers, said first and second resins being compatible such that said first and second plurality of fibrous layers are bondable to each other; supplying a third plurality of fibrous layers to said mold, said third plurality of fibrous layers comprising a non-woven network of high tenacity fibers impregnated with a third resin matrix, said high tenacity fibers comprising polyolefin fibers, said third plurality of fibrous layers overlying said second plurality of fibrous layers; and applying heat and pressure to said first plurality of fibrous layers, said second plurality of fibrous layers, and said third plurality of fibrous layers to thereby form said helmet shell. 